Capacitors adapted for acoustic resonance cancellation

ABSTRACT

An embodiment of the present invention provides a method, comprising reducing the losses due to electro-mechanical coupling and improving Q in a multilayered capacitor by placing a first capacitor layer adjacent at least one additional capacitor layer and sharing a common electrode in between the two such that the acoustic vibration of the first layer is coupled to an anti-phase acoustic vibration of the at least one additional layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/895,774 filed May 16, 2013, which is a continuation of U.S. patentapplication Ser. No. 11/890,901 filed Aug. 8, 2007 (now U.S. Pat. No.8,467,169), which is a continuation of U.S. patent application Ser. No.11/726,458 filed Mar. 22, 2007 (now U.S. Pat. No. 7,936,553). Thedisclosure of U.S. patent application Ser. No. 13/895,774 and U.S.patent application Ser. No. 11/890,901 are incorporated herein byreference in their entirety.

FIELD OF THE DISCLOSURE

Varactors are voltage tunable capacitors in which the capacitance isdependent on a voltage applied thereto. Although not limited in thisrespect, this property has applications in electrically tuning radiofrequency (RF) circuits, such as filters, phase shifters, and so on. Themost commonly used varactor is a semiconductor diode varactor, which hasthe advantages of high tunability and low tuning voltage, but sufferslow Q, low power handling capability, high nonlinearity and limitedcapacitance range. A new type of varactor is a ferroelectric varactor inwhich the capacitance is tuned by varying the dielectric constant of aferroelectric material by changing the bias voltage. Ferroelectricvaractors have high Q, high power handling capacity, good linearity andhigh capacitance range.

The use of barium titanate, strontium titanate, or barium strontiumtitanate (BST) of any composition including any doped BST formulation tomake tunable capacitors relies on the dielectric properties of theferroelectric material in the paraelectric phase. This means thedielectric constant of the material changes under the applied electricfield. As a capacitor, the capacitance at zero bias is a maximum and thecapacitance drops with applied voltage as illustrated in FIG. 1 at 100in capacitance 110 vs. volts 120. This change in capacitance allowsthese units to be used to create tunable circuits in filters, matchingnetworks, resonant circuits and other applications at frequencies fromaudio to RF and microwave.

The cross section of a typical capacitor consists of two (or more)conductive plates or electrodes with one or more layers of tunabledielectric material such as BST between them. The dielectric constant ofthe tunable material determines the capacitance as C=.epsilon.A/d, where.epsilon. is the dielectric constant of the tunable material, A is thearea of the electrodes and d is the separation of the electrodes andthickness of the tunable material. A DC voltage is applied to theelectrodes to induce an electric field in the tunable dielectric.

Since .epsilon. of the tunable material is a function of the electricfield which is E=V/d, then V=Ed and thus the capacitance is a functionof voltage. However, ferroelectric materials are also electrostrictive.As an electric field is applied, which lowers the dielectric constant,the piezoelectric constant of the material becomes non-zero. As aresult, the electric field is converted into a physical change of thelattice constants of the film. Simultaneous application of an AC signalto the material causes acoustic vibrations of atoms in the crystallinelattice and is called electromechanical coupling. Therefore any ACsignal on the tunable capacitor under bias produces an acousticresponse. At certain frequencies, determined by the layer thicknessesand materials in the capacitor stack, the acoustic response of thestructure will be resonant and the loss of the capacitor will increaseas energy is lost from the AC electrical signal into acousticvibrations.

This effect manifests itself as regions or frequencies where capacitorsexhibit high losses. Much design effort must be used to choose the layermaterials and their thicknesses to minimize or eliminate the acousticlosses at the desired frequencies of operation; however, it may beimpossible to completely eliminate the losses within the desiredfrequency band(s) because of conflicting performance requirements forthe device. This effect manifests over a wide range of frequencies up tomany Gigahertz—which is the usual range of frequencies used byapplications for these devices.

To illustrate this effect, an example of the frequency response of theQ-factor of a tunable capacitor from 100 MHz to 3 GHz is shown on FIG.2, generally as 200 [Q is a measure of the loss of the capacitor definedas Q=Xc/Rs where Xc=1/.omega.O and Rs is the series resistance].

At zero applied voltage 205, there is no generation of acousticvibrations by the tunable material and the Q versus frequency isrelatively smooth from 100 MHz to 3 GHz and rolls off from about 180down to 35.

At 30 volts applied voltage 215, this capacitor was designed to avoidacoustic loss effects up to about 1 GHz and the response is again fairlysmooth and flat dropping from about 150 to 70. Above 1 GHz, however, theresponse is no longer flat and the Q drops well below the Q at zerobias. The center frequency of the major resonances due to the acousticcoupling are noted on the chart at about 1.5 GHz (220), 1.7 GHz (225),1.85 GHz (230) and 2.8 GHz (235). These resonances prevent the capacitorfrom being used in those frequency ranges.

Thus, there is a strong need for voltage tunable capacitors adapted toreduce acoustic losses and improve Q.

BACKGROUND OF THE DISCLOSURE

An embodiment of the present invention provides a device, comprising amultilayered tunable dielectric capacitor, wherein the multilayers oftunable dielectric are adapted to be DC biased to reduce the dielectricconstant; and wherein the DC bias is arranged so that the number oflayers of tunable dielectric biased positively is equal to the number oflayers of tunable dielectric biased negatively.

An embodiment of the invention further provides a method, comprisingreducing the losses due to electro-mechanical coupling and improving Qin a multilayered capacitor by placing a first capacitor layer adjacentat least one additional capacitor layer and sharing a common electrodein between the two such that the acoustic vibration of the first layeris coupled to an anti-phase acoustic vibration of the at least oneadditional layer.

Still another embodiment of the present invention provides amultilayered tunable capacitor, comprising a first voltage tunabledielectric layer, at least one additional voltage tunable dielectriclayer adjacent to the first voltage tunable dielectric layer and sharinga common electrode in between the two, and wherein any acousticvibration of the first voltage tunable dielectric layer caused by theapplication of combined AC and DC voltages is coupled to a correspondingacoustic vibration caused by the application of the combined AC and DCvoltages to the at least one additional voltage tunable dielectriclayer, thereby reducing acoustic losses and improving Q.

Yet another embodiment of the present invention provides, a device,comprising a single layered varactor consisting of at least twocapacitors connected in series to an RF signal and adapted to reduceacoustic losses and improve Q. The adjacent electrodes of the at leasttwo capacitors may be positioned to vibrate in opposite phases therebyreducing acoustic losses and improving Q. Further, a DC bias may beapplied across the at least two capacitors from a top to a bottomelectrode.

Yet another embodiment of the present invention provides a method,comprising reducing the acoustic losses and improving Q in a singlelayered varactor by connecting at least two capacitors in series to anRF signal so that adjacent electrodes of the at least two capacitorsvibrate in opposite phase. In the present method, the DC bias may beapplied across the at least two capacitors from a top to a bottomelectrode and the at least two capacitors may produce acoustic waves ofthe opposite phase which cancel and wherein by placing a first capacitoradjacent to at least one additional capacitor, the acoustic wave of thefirst capacitor may be coupled to and cancel an opposite phase acousticwave of the at least one additional capacitor.

Still another embodiment of the present invention provides a device,comprising at least two capacitors connected in series to an RF signaland adapted to reduce acoustic losses and improve Q, wherein adjacentelectrodes of the at least two capacitors may be positioned to havemaximal interimposing of acoustic vibrations with opposite phasesthereby reducing acoustic losses and improving Q. The DC bias may beapplied across the at least two capacitors in opposite directions.

Yet another embodiment of the present invention provides a tunablecapacitor, comprising a plurality of voltage tunable dielectric layersacoustically coupled together and sharing a common conductive electrodebetween adjacent the tunable dielectric layers, a plurality of outerconductive electrodes on the outer surfaces of the tunable dielectriclayers forming a plurality of acoustically-coupled capacitors, and anapplied DC bias on each of the capacitors such that the number ofpositively-biased capacitors equals the number of negatively-biasedcapacitors. The present device may further comprise an applied RF signalbetween the top and bottom electrodes.

Lastly, an embodiment of the present invention may provide a tunablecapacitor, comprising multiple single-layer capacitors connected inseries to an RF signal, wherein the single-layer capacitors are in closelateral physical proximity and are acoustically coupled together andwherein a DC bias is capable of being applied to each capacitor suchthat the electric fields on equal numbers of the single-layer capacitorsare in opposite directions.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanyingdrawings. In the drawings, like reference numbers indicate identical orfunctionally similar elements. Additionally, the left-most digit(s) of areference number identifies the drawing in which the reference numberfirst appears.

FIG. 1 illustrates a typical C-V tuning curve of a voltage tunabledielectric capacitor;

FIG. 2 graphically depicts frequency vs. Q of a typical voltage tunablecapacitor at zero and 30 volts from 100 MHz to 3 GHz with losses due toacoustic vibration noted for 30 volts at 1.5, 1.7, 1.85 and 2.8 Ghz;

FIG. 3 illustrates a multilayered voltage tunable dielectric capacitoraccording to one embodiment of the present invention;

FIGS. 4 a and 4 b illustrate the configuration of a single-layeredvoltage tunable dielectric capacitor of one embodiment of the presentinvention;

FIG. 5 illustrates the Q vs. frequency from 100 MHz to 3 GHz of the twobias configurations of adjacent single layer capacitors of FIG. 4 of oneembodiment of the present invention; and

FIG. 6 graphically illustrates Q vs. DC bias when in phase and out ofphase of one multi-layer embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, components and circuitshave not been described in detail so as not to obscure the presentinvention.

An embodiment of the present invention provides a two layer capacitor inwhich the two layers produce acoustic vibrations of the opposite phasewhich cancel—although it is understood that the present invention is notlimited to two layers. By placing one capacitor in intimate physicalcontact with the other and sharing a common electrode in between thetwo, the acoustic vibration of one capacitor is coupled to acousticvibrations of the other. It is understood that the layers being adjacentin any arrangement is intended to be within the scope of the presentinvention. The structure is illustrated in FIG. 3, generally as 300.

In operation, in an embodiment of the present invention, a DC voltage310 may be applied from the center electrode 320 to the outer 2electrodes 330 and 340. The DC 310 can be either positive or negative,but it is illustrated as positive. As any RF (or AC signal of anyfrequency) signal may be applied between the two outer (top and bottomor side to side) electrodes of the two capacitors, the RF adds to the DCon one capacitor and subtracts on the other. As shown in the FIG. 3 at305, with zero DC, the two capacitors have no acoustic vibration and noacoustic loss. But as shown in FIG. 3, 350, the addition of DC biascauses the two tunable layers 355 and 360 to acoustically vibrate intime to the RF signal and the center electrode 365 will vibrate whilethe outside electrodes are relatively still, depending on the densityand thickness of the three metal electrodes. This is illustrated by thecurved shape of the center electrode 365 representing the physicaldisplacement at a moment in time. This means that the tunable layers arenot, (to first order), transmitting acoustic energy to the outer layers370 and 380 of the capacitor and subsequently into the rest of thesurrounding layer with their resonances causing extra losses. There maybe still vibrations within the two tunable layers 355 and 360 and thiswill incur some loss.

The result is that the two-layer (or multi-layer) structure shouldgreatly reduce the acoustic losses caused by acoustic resonance with thesurrounding layer structure. In addition, since the center layer ofmetal 365 is not carrying RF signals along its length, but only throughit from the bottom tunable layer 360 to the top tunable layer 355, itsresistivity can be much higher than the outside metal contacts whichmust support lateral conduction at low loss. This opens up the choice ofmiddle electrode materials to metals, metal oxides or other conductivematerials which may benefit the performance of the device and withstandthe processing of the capacitor stack.

Turning now to FIGS. 4 a and 4 b, is an illustration of theconfiguration of a single-layered voltage tunable dielectric capacitorconsisting of two capacitors connected in series to the RF signalaccording to one embodiment of the present invention and illustratingthe opposite direction of movement of the adjacent electrodes (FIG. 4 a)and the same direction of movement of the adjacent electrodes (FIG. 4 b)due to the vibration of the electrodes when the same DC bias is appliedacross both capacitors from top to bottom electrode (FIG. 4 a) and whenDC bias is applied from the top electrode of the left capacitor to thebottom electrode and then to the top electrode of the right capacitor.

The original observation of the effect of bias direction on the Qresponse of capacitors 405 and 410 was physical movement 415 ofcapacitor 1 (405) with DC=+volts 430 applied to top electrode 425relative to DC=0 volts at common bottom electrode 445; and physicalmovement 420 of capacitor 2 (410) with DC=+volts 435 applied to topelectrode 440 relative to DC=0 volts at common electrode 445, which ledto an even-numbered (such as 2) multilayer structure, was when biasingtwo capacitors 405 and 410 sitting side by side in close proximity. Thetwo capacitors 405 and 410 are biased such that one will be vibrating inone phase while the other is vibrating in the opposite phase because ofthe RF 450 and DC bias 430 and 435 polarities as shown in FIG. 4 a.Sandwiched between both top electrodes 425 and 440 and bottom electrode445 is a tunable dielectric material 450 such as Parascan® voltagetunable dielectric material or any other ferroelectric material(including those in paraelectric state), which may be placed abovesubstrate 455.

As shown in FIG. 4 b, when the DC voltages 405 and 470 were changed tobias one from +V to 0 volts and then from +V to +2 V, both capacitors485 and 490 vibrate together in phase.

Turning now to FIG. 5 at 500, the measured results show the out of phasebias condition 505 and in phase bias condition 510, and the measured Q515. Note the response peaks labeled 1 (520), 2 (530), 3 (540) and 4(550) which now appear when the two capacitors' acoustic response is inphase. These indicate the close proximity of the two capacitors allowsthe acoustic movement to cancel with the normal 15 volt bias but addwhen biased in phase.

As graphically depicted in FIG. 6 at 600, in an embodiment of thepresent invention, measurements of a 2-layer capacitor confirmed theexpected acoustic cancellation. The curve 610 at zero bias shows noacoustic resonances. The curve at 620, which depicts the measurementwith the two caps biased in phase, shows very substantial acousticresonance and loss from 100 MHz to 3 GHz (615) including significantpeaks or valleys at about 180 MHz, 300 MHz, 1.4 GHz, 2 GHz and 2.5 GHz.The curve 630 for anti-phase bias has removed all major peaks from theresponse and is well behaved from 100 MHz to 3 GHz (615). (The twomeasured curves, 610 and 620, are measured on the same device just withdifferent bias directions).

Thus, to reiterate, the acoustic loss can be influenced by the phase ofthe acoustic vibrations in adjacent or acoustically-coupled layers ofmaterials. Further, acoustic cancellation may eliminate resonances andloss when two layers of tunable material are placed on top of each otherand biased for anti-phase response. Again, although the presentembodiment of the present invention describes a two layer embodiment,any number of layers and, more preferably, any equal number of tunabledielectric layers with opposite DC bias should produce cancellation.

The cancellation may not eliminate all acoustic loss or at allfrequencies as the tunable dielectric material and the center electrodelayer may still vibrate and generate losses, although at reduced levelsat most frequencies. The two layer structure allows the resistivityrequirements of the center layer to be relaxed and a wider range ofmaterials may be used. Different materials in the center conductor willchange the frequency and extent of the intrinsic loss of the two-layerstructure allowing the device to be adapted for different frequencybands of operation.

Throughout the aforementioned description, BST can be used as a tunabledielectric material that may be used in a tunable capacitor of thepresent invention. However, the assignees of the present invention,Paratek Microwave, Inc. and Gennum Corporation have developed andcontinue to develop other tunable dielectric materials that may beutilized in embodiments of the present invention and thus the presentinvention is not limited to using BST material. One family of tunabledielectric materials may be referred to as Parascan®.

The term Parascan® as used herein is a trademarked term indicating atunable dielectric material developed by Paratek Microwave Inc.Parascan® tunable dielectric materials have been described in severalpatents. Barium strontium titanate (BaTiO₃—SrTiO₃), also referred to asBSTO or BST, is used for its high dielectric constant (200-6,000) andlarge change in dielectric constant with applied voltage (25-75 percentwith a field of 2 Volts/micron). Tunable dielectric materials includingbarium strontium titanate are disclosed in U.S. Pat. No. 5,312,790 toSengupta, et al. entitled “Ceramic Ferroelectric Material”; U.S. Pat.No. 5,427,988 by Sengupta, et al. entitled “Ceramic FerroelectricComposite Material-BSTO—MgO”; U.S. Pat. No. 5,486,491 to Sengupta, etal. entitled “Ceramic Ferroelectric Composite Material-BSTO—ZrO₂”; U.S.Pat. No. 5,635,434 by Sengupta, et al. entitled “Ceramic FerroelectricComposite Material-BSTO-Magnesium Based Compound”; U.S. Pat. No.5,830,591 by Sengupta, et al. entitled “Multilayered FerroelectricComposite Waveguides”; U.S. Pat. No. 5,846,893 by Sengupta, et al.entitled “Thin Film Ferroelectric Composites and Method of Making”; U.S.Pat. No. 5,766,697 by Sengupta, et al. entitled “Method of Making ThinFilm Composites”; U.S. Pat. No. 5,693,429 by Sengupta, et al. entitled“Electronically Graded Multilayer Ferroelectric Composites”; U.S. Pat.No. 5,635,433 by Sengupta entitled “Ceramic Ferroelectric CompositeMaterial BSTO—ZnO”; U.S. Pat. No. 6,074,971 by Chiu et al. entitled“Ceramic Ferroelectric Composite Materials with Enhanced ElectronicProperties BSTO Mg Based Compound-Rare Earth Oxide”. These patents areincorporated herein by reference. The materials shown in these patents,especially BSTO—MgO composites, show low dielectric loss and hightunability. Tunability is defined as the fractional change in thedielectric constant with applied voltage.

Barium strontium titanate of the formula Ba.sub.xSr.sub.1-xTiO3 is apreferred electronically tunable dielectric material due to itsfavorable tuning characteristics, low Curie temperatures and lowmicrowave loss properties. In the formula BaxSr1-xTiO3, x can be anyvalue from 0 to 1, preferably from about 0.15 to about 0.6. Morepreferably, x is from 0.3 to 0.6.

Other electrically tunable dielectric materials may be used partially orentirely in place of barium strontium titanate. An example is(Ba.sub.xCa.sub.1-x)TiO.sub.3. Additional electronically tunableferroelectrics include any electrically tunable compositions ofperovskites such as, NaNO₃, KNbO₃, BaTiO₃, SrTiO₃, CaTiO₃, members ofthe lead titanate family such as PbTiO₃, Pb(Zr_(x)Ti_(1-x))O₃ (PZT),(Pb,Sr)(Zr_(x)Ti_(1-x))O₃, (Pb,La)(Zr_(x)T_(1-x))O₃ (PLZT),niobate-tantalate family such as LiTaO₃, PbNb₂O₆, KSr(NbO₃), LiNbO₃,K(Ta_(1-x)Nb_(x))O₃, PbTa₂O₆ KDP (KH₂PO₄) layeredperovskites/Aurivillius phases such as SrBi₂Ta₂O₉ (SBT), tungsten-bronzestructures (PbTa₂O₆), phosphates such as KH₂PO₄ (KDP), fluorides such asBaMgF₄ and mixtures and compositions thereof. Also, these materials canbe combined with low loss dielectric materials, such as magnesium oxide(MgO), aluminum oxide (Al₂O₃), and zirconium oxide (ZrO₂), and/or withadditional doping elements, such as manganese (Mn), iron (Fe), andtungsten (W), or with other alkali earth metal oxides (i.e. calciumoxide, etc.), transition metal oxides, silicates, niobates, tantalates,aluminates, zirconates, nitrides and titanates to further reduce thedielectric loss.

In addition, the following U.S. patents and patent Applications,assigned to the assignee of this application, disclose additionalexamples of tunable dielectric materials: U.S. Pat. No. 6,514,895,entitled “Electronically Tunable Ceramic Materials Including TunableDielectric and Metal Silicate Phases”; U.S. Pat. No. 6,774,077, entitled“Electronically Tunable, Low-Loss Ceramic Materials Including a TunableDielectric Phase and Multiple Metal Oxide Phases”; U.S. Pat. No.6,737,179 filed Jun. 15, 2001, entitled “Electronically TunableDielectric Composite Thick Films And Methods Of Making Same; U.S. Pat.No. 6,617,062 entitled “Strain-Relieved Tunable Dielectric Thin Films”;U.S. Pat. No. 6,905,989, filed Apr. 31, 2002, entitled “TunableDielectric Compositions Including Low Loss Glass”; U.S. patentapplication Ser. No. 10/991,924, filed Nov. 18, 2004, entitled “TunableLow Loss Material Compositions and Methods of Manufacture and UseTherefore” These patents and patent applications are incorporated hereinby reference.

The tunable dielectric materials can also be combined with one or morenon-tunable dielectric materials. The non-tunable phase(s) may includeMgO, MgAl₂O₄, MgTiO₃, Mg₂SiO₄, CaSiO₃, MgSrZrTiO₆, CaTiO₃, Al₂O₃, SiO₂and/or other metal silicates such as BaSiO₃ and SrSiO₃. The non-tunabledielectric phases may be any combination of the above, e.g., MgOcombined with MgTiO₃, MgO combined with MgSrZrTiO₆, MgO combined withMg₂SiO₄, MgO combined with Mg₂SiO₄, Mg₂SiO₄ combined with CaTiO₃ and thelike.

Additional minor additives in amounts of from about 0.1 to about 5weight percent can be added to the composites to additionally improvethe electronic properties of the films. These minor additives includeoxides such as zirconates, tannates, rare earths, niobates andtantalates. For example, the minor additives may include CaZrO₃, BaZrO₃,SrZrO₃, BaSnO₃, CaSnO₃, MgSnO₃, Bi₂O_(3/2)SnO₂, Nd₂O₃, Pr₇O₁₁, Yb₂O₃,Ho₂O₃, La₂O₃, MgNb₂O₆, SrNb₂O₆, BaNb₂O₆, MgTa₂O₆, BaTa₂O₆ and Ta₂O₃.

Films of tunable dielectric composites may comprise Ba_(1-x)SrxTiO₃, incombination with at least one non-tunable dielectric phase selected fromMgO, MgTiO₃, MgZrO₃, MgSrZrTiO₆, Mg₂SiO₄, CaSiO₃, MgAl₂O₄, CaTiO₃,Al₂O₃, SiO₂, BaSiO₃ and SrSiO₃. These compositions can be BSTO and oneof these components, or two or more of these components in quantitiesfrom 0.25 weight percent to 80 weight percent with BSTO weight ratios of99.75 weight percent to 20 weight percent.

The electronically tunable materials may also include at least one metalsilicate phase. The metal silicates may include metals from Group 2A ofthe Periodic Table, i.e., Be, Mg, Ca, Sr, Ba and Ra, preferably Mg, Ca,Sr and Ba Preferred metal silicates include Mg2SiO4, CaSiO3, BaSiO3 andSrSiO3. In addition to Group 2A metals, the present metal silicates mayinclude metals from Group 1A (alkalai metals), i.e., Li, Na, K, Rb, Csand Fr. For example, alkalai metal silicates may include sodiumsilicates such as Na2SiO3 and NaSiO3-5H2O, and lithium-containingsilicates such as LiAlSiO4, Li2SiO3 and Li4SiO4. Metals from Groups 3A,4A and some transition metals of the Periodic Table may also be suitableconstituents of the metal silicate phase. Additional metal silicates mayinclude Al2Si2O7, ZrSiO4, Ka1Si3O8, NaAlSi3O8, CaAl2Si2O8, CaMgSi2O6,BaTiSi3O9 and Zn2SiO4. The above tunable materials can be tuned at roomtemperature by controlling an electric field that is applied across thematerials.

In addition to the electrically tunable dielectric phase, theelectrically tunable materials can include at least two additional metaloxides. The additional metal oxides may include alkalai earth metalsfrom Group 2A of the Periodic Table, i.e; Mg, Ca, Sr, Ba, Be and Ra Theadditional metal oxides may also include metals from Group 1A, i.e., Li,Na, K, Rb, Cs and Fr, preferably Li, Na and K. Metals from other Groupsof the Periodic Table may also be suitable constituents of the metaloxide phases. For example, refractory metals such as Ti, V, Cr, Mn, Zr,Nb, Mo, Hf, Ta and W may be used. Furthermore, metals such as Al, Si,Sn, Pb and Bi may be used. In addition, the metal oxide phases maycomprise rare earth metals such as Sc, Y, La, Ce, Pr, Nd and the like.

The additional metal oxides may include, for example, zirconates,silicates, titanates, aluminates, stannates, niobates, tantalates andrare earth oxides. Preferred additional metal oxides include MgO, CaO,ZrO₂, Al₂O₃, WO₃, SnO₂, SnO₂ Ta₂O₅, MnO2, PbO, Bi₂O₃ and La₂O₃ (or anyother rare earth oxide) in any concentration

Multilayer capacitors with different biasing methods have been describedin other patents assigned to Gennum Corporation; U.S. Pat. No. 5,745,335and U.S. Pat. No. 6,411,494. These patents are applicable to themulti-layered structures described in this invention.

What is claimed is:
 1. A device comprising: a matching network includingfirst and second voltage tunable capacitors, wherein the first voltagetunable capacitor has a first electrode, wherein the second voltagetunable capacitor has a second electrode, wherein the first and secondelectrodes are positioned in proximity to each other, and wherein thefirst and second voltage tunable capacitors share a common electrode;and a bias element coupled with the matching network, wherein the biaselement applies a bias voltage to the first electrode of the firstvoltage tunable capacitor and to the second electrode of the secondvoltage tunable capacitor causing the first and second voltage tunablecapacitors to vibrate in opposite phase to each other substantiallycancelling first and second electro-mechanical vibrations generated bythe first and second voltage tunable capacitors, wherein the commonelectrode is unbiased, and wherein the common electrode has a higherresistivity than the first and second electrodes.
 2. The device of claim1, wherein the common electrode is positioned opposite to the first andsecond electrodes.
 3. The device of claim 1, wherein the first andsecond voltage tunable capacitors comprise a single tunable dielectriclayer positioned between the common electrode and the first and secondelectrodes.
 4. The device of claim 3, wherein the first and secondelectrodes are positioned along an outer surface of the single tunabledielectric layer.
 5. The device of claim 3, wherein the single tunabledielectric layer comprises barium strontium titanate.
 6. The device ofclaim 1, wherein the first and second voltage tunable capacitorscomprise a substrate, and wherein the common electrode is positioned onthe substrate.
 7. The device of claim 6, wherein the common electrode issurrounded by a single tunable dielectric layer and the substrate. 8.The device of claim 1, wherein the first and second voltage tunablecapacitors comprise a single tunable dielectric layer and a substrate,and wherein only a portion of the single tunable dielectric layer ispositioned on the substrate.
 9. A device comprising: first and secondvoltage tunable capacitors that share a common electrode; and a biaselement that applies a first bias voltage to a first electrode of thefirst voltage tunable capacitor and that applies a second bias voltageto a second electrode of the second voltage tunable capacitor, whereinthe common electrode is unbiased, and wherein the applying of the firstand second bias voltages causes the first and second voltage tunablecapacitors to vibrate in opposite phase to each other, wherein the firstand second voltage tunable capacitors are a multi-layered stackeddielectric structure including multiple layers of dielectric material,and wherein the common electrode has a higher resistivity than the firstand second electrodes.
 10. The device of claim 9, wherein the multiplelayers of the dielectric material are an even number of layers.
 11. Thedevice of claim 9, wherein the multiple layers of the dielectricmaterial are greater than or equal to two layers.
 12. The device ofclaim 9, wherein the first and second voltage tunable capacitorscomprise barium strontium titanate.
 13. The device of claim 9, whereinthe common electrode comprises a metal oxide.
 14. The device of claim 9,wherein the common electrode is positioned in a middle portion of themulti-layered stacked dielectric structure.
 15. A device comprising: aplurality of voltage tunable capacitors that share a common electrode;and a bias element that applies bias voltages to other electrodes of theplurality of voltage tunable capacitors, wherein the applying of thebias voltages causes pairs of the plurality of voltage tunablecapacitors to vibrate in opposite phase to each other, wherein theplurality of voltage tunable capacitors are a multi-layered stackeddielectric structure including multiple layers of dielectric material,and wherein the common electrode has a higher resistivity than the otherelectrodes.
 16. The device of claim 15, wherein the multiple layers ofthe dielectric material are an even number of layers.
 17. The device ofclaim 15, wherein the multiple layers of the dielectric material aregreater than or equal to two layers.
 18. The device of claim 15, whereinthe plurality of voltage tunable capacitors comprise barium strontiumtitanate.
 19. The device of claim 15, wherein the common electrodecomprises a metal oxide.
 20. The device of claim 15, wherein the commonelectrode is positioned in a middle portion of the multi-layered stackeddielectric structure.